Certain industrial and public service facilities--such as power generating stations, pumped storage plants, public water supplies, ore processing plants, and pumped irrigation canals--require large supplies of water for their operations. As a rule, the required supplies of water are drawn off or diverted from such natural sources as rivers, lakes, estuaries, and coastal seawaters.
Fish that inhabit these natural water sources are regularly drawn into the intake structures of such facilities. Once indrawn, the fish tend to move with the water flow until they are blocked from further entrainment by barrier or "intake" screens. These barrier screens are universally employed as the means for preventing the passage of debris into the circulating systems of pumping facilities. Some barrier screens are stationary, but many are moved, or caused to "travel", in a vertical direction around driving sprockets after the manner of part of an endless belt. Whether stationary or travelling, the barrier screens prevent the further entrainment of indrawn fish (except for larvae or juveniles so small as to be extruded through the screen meshes). The indrawn fish remain trapped in the screenwells of these intake structures if not otherwise removed, eventually suffering injury or death from being pressed against a barrier screen or into its meshes by the force of the water flow.
Because actively swimming fish tend to align themselves parallel with the oncoming flow and headmost into it, they are moved rearwards toward the barrier screen. As the fish come into tailfirst contact with the screen they dart out and tend to stand against the flow in the region just in front of the screenface. In so stemming the force of the oncoming flow, the fish increase their swimming efforts and become progressively exhausted by their increased rates of energy expenditures. Over the course of time the spent fish are pressed onto the barrier screen by the force of the flow and killed.
Many attempts have been made at reducing injury and death to fish drawn into water intake systems. Certain nonmechanical schemes have been employed with the thought to inducing the entry of fish into bypassing conduits or to frightening the fish away prior to entrapment. All known strategems of that kind--such as sound waves, bubble curtains, strobe lights, water jets, shock waves, chemical repellents, and electricity--have proved ineffective in full-scale systems.
Various mechanical devices have also been tried and found wanting, either through mechanical impracticalities or because of an ultimate lack of effectiveness in saving fish. In one experimental demonstration, for example, a travelling barrier screen was repositioned so as to move laterally across the flow, its frontmost side driven in the direction of a bypassing slot located at one end of the moving screen. Although effective in conveying small fish toward the bypassing slot, the device was found to be unsound at the scale of industrial intake structures. Mechanical limitations also prohibit the enlargement of such small-scale devices as wedge-wire cylinders and similar rotating mechanisms.
At some water intake facilities, vertical travelling screens have been equipped with troughs, the aim being the direct removal of fish through the scooping action of the troughs. Field tests on this modification have not shown it to be uniformly better at conserving fish than conventional travelling screens.
Some intake structures have been equipped with passive "guiding" barriers, usually in the form of vertical metal louvres or conventional barrier screens, placed diagonally across the intake flume and leading to a narrow bypassing slot located at the apex of the acute angle between the barrier and the wall of the flume. In tests on most louvre arrays, the majority of the test fish were drawn directly through the louvre openings and into the pumps of the intake system. Only when the louvre vanes were shaped in such a way as to create a strong local turbulence did the majority of the fish, in apparent reaction to the turbulent front, find their way to the bypassing slot. But turbulent louvre arrays have not been applied to industrial facilities because of the accompanying losses in pumping efficiency. The turbulence that impedes the passage of fish through the louvre openings also impedes the flow of water into the intake system, thus decreasing the volumetric intake to unacceptable levels of efficiency.
With conventional barrier screens set at an angle to the flow--as with the same screens set normal to the flow--the indrawn fish tend to stand head-on against the current, and only through chance do they encounter the bypassing slot. Owing to the randomness of fish movement and the infrequency of encounter with the bypassing slot, the fish mortalities associated with angled barrier screens are usually very high.
The objective with this invention, therefore, is the creation of a system for diverting fish from pumped intake structures and returning them unharmed to the natural water bodies from whence they came.
A further objective of this invention is to make possible a method for herding fish rapidly into zones of withdrawal and away from barrier screens, against which they would otherwise be drawn and killed.
A further objective associated with this invention is the conserving of fishlife and the maintaining of indigenous species in their natural habitats despite the presence of large pumping facilities.